A person's Respiratory Quotient (RQ) is a useful indicator of the person's physiological condition. One particular indication of the RQ is the food substrate being metabolized. An RQ of 1.0 indicates pure carbohydrate metabolism, while an RQ of 0.7 indicates pure fat metabolism. RQs between 1.0 and 0.7 indicate a mixture of energy sources. The following table, taken from a book by Denise Schwartz entitled Resting Energy Expenditure, 1998, VacuMed, with references to Frer and Mullen, Beside measurement of resting energy expenditure and respiratory quotient via indirect calorimetry, Nutr Clin Prac, February, 1986, Vol. 1, pages 43-49; Matarese, Indirect calorimetry: technical aspect, J Am Diet Assoc, 1997, Vol. 97 (supp. 2), pages S154-S160; and McClave and Snider, Use of indirect calorimetry in clinical nutrition, Nutr Clin Prac, October, 1992, Vol. 7, pages 207-221, illustrates the RQ for different energy sources and conditions:
Energy Source - ConditionRQProlonged Ketosis<.70Pure Fat Metabolism.70Normal Mixed Energy SourcesTypically .85Pure Carbohydrate Metabolism1.00Fat Storage>1.00
Weight loss, or more specifically fat loss, requires the metabolism of fat. Typically, when following any one of the many creditable weight loss programs such as the Atkins diet, a person's diet and exercise are adjusted such that body fat is metabolized in the resting state. As evidenced by the above table, a diet and exercise program weighted toward fat metabolism produces an RQ closer to 0.7 than 1.0. When the dieter's resting RQ is below 0.85, the dieter knows that he or she is metabolizing fat. In particular, the lower the dieter's RQ value, the higher percentage of fat as opposed to carbohydrate is being metabolized by the dieter. Rapid feedback in the form of RQ change an hour or so after eating or exercise allows diet program adjustment without having to wait for longer term indications such as weight loss or dimension reduction.
The respiratory quotient (RQ) is defined as the ratio of carbon dioxide (CO2) production (QCO2) to oxygen consumption (QO2). QCO2 and QO2 can be, and are routinely, measured clinically using sophisticated metabolic monitoring systems. Unfortunately, such monitoring systems are too expensive and too complicated for use by the typical dieter for home monitoring of the progress of a diet. An improved method is desired that permits a user to estimate his or her RQ when in the resting condition using an apparatus that is substantially less expensive and easier to use than a conventional metabolic monitor, thereby allowing for more widespread use of such a measurement at lower cost to the dieter. In particular, a method and apparatus is desired that permits dieters to quantify when and to what degree they are metabolizing fat in the resting state.
Methods and apparatus for assisting with caloric intake are known. For example, U.S. Pat. No. 6,478,736 discloses an “Integrated Calorie Management System” that is representative of a recent trend in dietary monitoring. The disclosed calorie management system includes a device known as a Gas Exchange Monitor (GEM) that is used in a method for measuring resting metabolic rate (RMR). The notion of this patent is that by knowing the resting metabolic rate and adding to it the estimated calories burned in daily exercise the required caloric intake can be measured. Once the required caloric intake is known, the caloric content of food can be estimated and the diet constructed such that fewer calories are consumed than are expended to bring about weight loss. The GEM is described as a critical element of the system since the RMR varies from individual to individual and even from day to day within one person. However, this patent does not teach the measurement of fat metabolism or any simplified method of quantifying fat metabolism.
Methods and apparatus for measuring Resting Energy Expenditure are also known. For example, U.S. Pat. No. 6,572,561 discloses a simplified apparatus for measuring Resting Energy Expenditure. In the disclosed system, a CO2 sensor and a flow sensor are combined and oxygen consumption is measured without actually measuring oxygen concentration. In addition, RQ is also computed without measuring oxygen consumption using an oxygen sensor. Instead, the flow sensor and CO2 sensor are used to measure RQ. However, both sensors required in this device are required to react quickly to flow rate and concentrations changes and, accordingly, are relatively high performance devices that are quite expensive. This device has the advantage that high performance CO2 sensors are relatively simpler and less expensive than high performance oxygen sensors. However, the added requirement of a high performance flow sensor for measuring RQ and the difficult response time demands make such a device too costly and complicated for home use. Moreover, flow sensors tend to be relatively inaccurate and are responsible for much of the measurement error of such devices.
U.S. Pat. No. 4,197,857 discloses a microprocessor based clinical instrument designed to precisely measure metabolic parameters including RQ. This patent discloses the classical method of RQ measurement incorporating precision O2, CO2 and flow sensors. The precision flow sensor is implemented as a relatively low cost disposable. However, even though it may be a precision device, the flow sensor remains a source of a significant portion of the measurement error.
U.S. Pat. No. 5,705,735 discloses a high precision clinical metabolic measurement system that is optimized for use with a person on a ventilator. This patent teaches the value of RQ in adjusting the nourishment of a critically ill person, thereby supporting the notion that RQ is valuable to a dieter. However, this patent does not teach a simplified device or method for measuring resting RQ outside of a traditional clinical setting.
Thus, a need exists in the art for a method that permits a dieter to measure his or her respiratory quotient using a relatively inexpensive and simple to use device in a non-clinical setting. The present invention addresses this need in the art.